British Prime Minister Margaret Thatcher was advised that Canadians’ sensitivity “is a fact of life” spurred on by the country’s “ham-fisted neighbour to the south,” in a set of confidential briefing notes prior to her Canadian visit in 1983.

Government files from 30 years ago, released this week by the British National Archives, included two telegrams dated Sept. 1 and Sept. 19, 1983 to No. 10 Downing Street to prepare Thatcher for her visit to Ottawa, Toronto and Edmonton. In them, Canada is described as a country that is “dominated commercially and culturally by the United States, but is inclined to resent this.”...